Annular blowout preventers have long been used on wells to provide a means for controlling blowouts. Metal inserts have been used on the upper and lower surfaces of the resilient packing annulus to provide support for such annulus as shown in U.S. Pat. No. 4,310,139. Such a preventer is actuated by axial loading of the resilient packing annulus. One problem encountered with such structure is that while one set of the support inserts moves into position to support the resilient annulus when the preventer is closed, the set of support inserts on the opposite side of the annulus may not always move fully into their preferred support position when actuated. Under these conditions the inner portion of the packer is not sufficiently confined to effect an acceptable seal.
Other devices have included projections on the plates embedded in the resilient packer annulus as an attempt to solve this problem to ensure that all of the insert plates move inward uniformly to provide the desired support allowing proper sealing of the packing annulus.